The pallet full of mystery boxes above could be filled with USB drives, keychains, or even snap bracelets, though it's a good bet it's shiny, expensive gadgets instead.

Google teased the rather nondescript, and otherwise unexciting collection of boxes on Google+ Friday afternoon, saying only "Boom. Chrome swag has arrived. #io13."

Whatever's inside is expected to be handed out to the 5,000 developers who signed up to attend Google I/O, which kicks off on Wednesday. In the past, Google has handed out a dizzying array of gadgetry to attendees, from Android phones to tablets, notebook computers, and, in last year's case the ill-fated Nexus Q home entertainment device.